I. Field of the Invention
This invention relates generally to electrosurgical apparatus, and more particularly to an improved handle device for a polypectome snare for use in excising polyps from an internal body cavity.
II. Discussion of the Prior Art
Polypectome snares are electrically powered devices designed for the removal of small growths from the lining of internal body cavities. The growth, or polyp, is encircled by the snare, then sheared off by electrocautery action.
The U.S. Pat. No. 4,905,691 of Rydell describes a bipolar polypectome snare in which the electrodes are insulated from one another by means of two concentric tubes. One tube encloses one electrode wire and this tube is positioned within the second tube which also encloses the other wire. An RF voltage is applied by a power supply such that when the loop of the snare is placed around a polyp and tightened, the polyp is excised. Another design of a bipolar polypectome snare is disclosed in co-pending application Ser. No. 07/554,835 of Rydell, wherein both electrode wires are housed in tubing. This tubing may either be a solid rod in which parallel bores receive the electrode wires or it may be two, separate small diameter tubes, each of which contains an electrode wire and which are disposed inside a third tube which serves as a retainer.
In U.S. Pat. No. 4,311,143 to Komiya, there is described the construction of a bipolar electrosurgical polypectome snare which comprises an elongated, flexible plastic tube whose outside diameter is sufficiently small to permit it to pass through the lumen of an endoscope and affixed to the distal end of the tube is a first electrode in the form of an annular metallic cap. The second electrode comprises a wire loop which can be extended and retracted relative to the distal end of the tubular body. When inserted through the lumen of an endoscope, it can be made to loop around the polyp to be excised and then by manipulating a hand grip member, the loop can be drawn tight about the neck of the polyp as RF energy is applied between the annular cap and the wire loop. The tissue comprising the polyp completes the circuit between the two electrodes and with sufficient power applied, the stem of the polyp will eventually be cut through. The hand grip member of the instrument is not described in detail.
The Treat U.S. Pat. No. 4,493,320 describes a polypectome snare having a bi-lumen tube dimensioned to fit through an endoscope. It has a pair of wires routed through each of the lumens which extend beyond the distal end thereof, where they are joined with an insulating tip member to form a loop. Thus, portions of the wires themselves become the active bipolar pair. The hand grip used to open and close the loop consists of prongs which extend from the face of a slide block that is positioned in the base of the device. In this manner, the block can be manually operated to slide along the longitudinal axis of the base. As the handle moves the slide block, the snare wires are caused to slide in the tube so as to expand or retract the surgical loop that extends from the distal end of the tube.
The afore-referenced Rydell Patent '691 and pending application '835 teach a polypectome snare with bipolar electrodes in which a pair of wire electrodes is routed through the lumens of first and second tubes. These tubes are dimensioned to fit inside the lumen of an endoscope. When the first tube is placed inside the second tube, rotation of the proximal end of one of the two wires is permitted but an attempt to rotate the loop does not cause twisting of the wires as it did in the prior art. Furthermore, the handle was redesigned to include finger holes affixed to a slide block and to the base of the device. The thumb is inserted into the hole provided at the proximal end of the base. The index and middle fingers are then inserted into the two holes provided in the slide block. As the slide block is opposably advanced, the loop of the snare is caused to open, since the electrode wires are mounted on the slide block. Conversely, the loop will close around the base of the polyp and cauterize it as the two sets of finger holes are drawn together.
Problems exist with the Treat and Rydell devices. In the Treat U.S. Pat. No. 4,493,320, an elongated base member is fitted with a slide block which includes a handle. The handle consists of two prongs and a loop. It is possible that the surgeon's hand could slip on the prongs as his attention is drawn away from his hand, as when he views the endoscope screen.
The Rydell improvement in U.S. Pat. No. 4,905,691 addressed this tendency for slipping by providing secure finger holes. The surgeon is then free to focus his attention on polyp removal as he is guided by viewing the endoscope screen. The co-pending improvement provides the same functional handle which did not short, but both are expensive and labor-intensive to produce, thus precluding disposability.
The present invention is applicable to all of these devices, since it provides an improved handle that will interface with each of applicant's earlier designs. This is significant because it has been found that utilization of bipolar electrodes instead of a monopolar arrangement has, in the past, created difficulty in proper handle design. Specifically, the handle must be designed in a manner that prevents any rotation of the wire which might permit arcing or cause a dead short proximal of the working loop or snare. This must be accomplished economically yet in a way that permits easy assembly.